Process for smelting ore with a cyclone combustor



Nov. 9, 1965 H. P. HUDSON 3,216,818

PROCESS FOR SMELTING ORE WITH A CYCLONE COMBUSTOR Filed Oct. 21, 1964 2 Sheets-Sheet 1 H06 Fi Hudsan XIMJ Nov. 9,1965 H. P. HUDSON 3,216,313

PROCESS FOR SMELTING ORE WITH A CYCLONE COMBUSTOR Filed Oct. 21, 1964 2 Sheets-Sheet 2 United States Patent Cfilice 32%,818 Patented Nov. 9, 1965 3,216,818 PROCESS FOR SMELTENG ORE WTTH A CYCLONE COMBUSTGR Hugh Paul Hudson, Ottawa, Ontario, Canada, assignor to Her Majesty the Queen in- Right of Canada as represented by the Minister of Mines and Technical Surveys Filed Oct. 21, 1964, Ser. No. 405,466 3 Claims. (Cl. 75-40) This is a continuation-in-part of application Serial No. 855,955, filed November 25, 1959 (now abandoned), which was a continuation-in-part of application Serial No. 654,- 03 1, filed April 19, 1957 and now abandoned.

This invention relates to a process for smelting ores.

Ores such as iron ores usually comprise metal in an oxidized form and it is necessary that the ores be reduced and that the metal be separated from gangue components. A blast furnace is customarily used to achieve the reduction and separation of the metal.

Blast furnaces suifer from several disadvantages. The fuel used in blast furnace practice must be carefully selected to minimize impurities such as sulfur which would result in an unduly high sulfur content in the end product. Coal cannot be used but must be coked with consequent high process and equipment costs. The coke not only has to be low in impurities but also has to have physical characteristics such that it will retain its shape under pressures imposed by heavy loads. High pressures are necessary to maintain the blast through the furnace with consequent high power consumption. The heat losses during blast furnace operation are exceedingly high, even where elaborate heat exchangers and the like are used. There is a large carry over of dust which has to be removed and sintered to avoid undue losses. Blast furnaces also have the defect that small units cannot be operated on a competitive basis. This results in substantial transportation costs, hampers the development of new sources of supply and discourages the erection of new plants to satisfy the demands of an expanding economy.

A prime object of one aspect of this invention is to provide a process for reducing and separating the metallic values of an ore having an increased efficiency in comparison with a blast furnace and in which, more specifically, there are lower heat losses, lower power consumption and higher output for an equivalent equipment investment and in which there are the possibilities of saving cost by using even a low grade of coal in place of coke and of economically operating comparatively small units.

In accordance with this aspect of the present invention a process is provided comprising the steps, in sequence, of

(l) continuously feeding a carbon-containing material to a combustion zone;

(2) completely burning said carbon-containing material in said combustion zone in a helically swirling stream to produce combustion products consisting essentially of CO and H 0, said combustion products being at a temperature in excess of 3000 F.;

(3) passing said combustion products in a swirling stream and while still at a temperature in excess of 3000 F. into a second zone;

(4) continuously feeding a finely divided mixture of ore containing metal oxide, slag forming constituents, and carbon-containing material into said stream of hot combustion products in said second zone downstream of said entry point of said hot combustion products, thereby converting said second zone into a reducing zone;

(5) continuously reacting said mixture in said stream in said reducing zone whereby at least 50% of the metal oxide is reduced to metal and wherein slag forming constituents are melted;

(6) continuously collecting liquids and solids separating from said stream as a mixture of slag, ore, carbon-containing material and metal;

(7) continuously passing said swirling stream over the surface of said mixture thereby completing reduction of the metal oxide in said ore to metal; and finally (8) continuously recovering the thereby produced metal. In other words, by the process of the present invention a stream of gas is generated having a sufiiciently high temperature to melt the components of metal bearing ores so that, with an iron ore, droplets initially largely of iron oxide are formed in the gas stream. The reduction reaction involved in the process of this invention is a high temperature reduction of iron oxide into a liquid iron phase and contrasts with that carried out in the blast furnace, where the lump ore is largely reduced to solid iron before melting in the furnace hearth. The lowest melting points of the following phases restrict the minimum temperature that can be used: ferrous oxide, 1370 C.; ferrous silicate system, 1180 C.; pure iron, 1535 C.; and liquid iron containing the maximum carbon content of 4.3%, 1130 C. The lowest reduction temperature that can be used to meet the requirement that the iron be liquid depends on the carbon content of the iron produced, that is the carbon content of the iron in the particles held in the gas stream, not in the bulk collected iron phase in the furnace hearth. The highest temperature necessary is, then, 1535 C. for the case where pure iron is produced. The normal operating range for reducing iron oxide such as hematate or magnetite is above 1200 C. and preferably above 1400 C. Preferably the stream of gas is generated by a cyclone combustor so that it swirls in a helical path. Fuel and an oxygen-containing gas, such as oxygen or air, are supplied to the cyclone combustor in proportion such that said stream of gas has a neutral or slightly oxidising atmosphere and combustion is completed with maximum efiiciency. This results in a complete burning of the fuel (usually powdered coal) in a helically swirling stream to carbon dioxide and water.

An intimate mixture of finely divided ore (the term ore is also intended to include ore concentrates), slag forming components, such as limestone, and a carbon-containing material such as coal (oil or natural gas) is directed transversely into said stream downstream of the zone where the fuel is completely burned so as to form a reducing zone. For example, the intimate mixture may be allowed to fall by gravity into the gas stream. The high temperature gases of the gas stream in conjunction with the carbon-containing material, i.e. coal, added in the reducing zone achieve a partial reduction of the metal oxides in the ore. The mixture of ore and carbon-containing material, i.e. coal, is formed of particles some of which are larger than others. The smaller ones are sufliciently light to be carried along in the gas stream and the ore in these particles undergoes reduction in the gases comprising the carbon monoxide formed by combustion and any hydrocarbons present such as those generated by distillation of the introduced carbon-containing material, i.e. coal. The larger particles are, however, too heavy to remain in the stream and due to the swirling movement of the gases are thrown onto the walls of the reducing zone, where they become partially embedded in the film of molten matter (which may include slag carried over from the cyclone combustion in the combustion zone) already present on these walls. The reduction zone is preferably circularly shaped in cross section with its axis aligned in the main direction of progression of the gas stream. The particles on the walls are in good surface contact with the gas stream and quickly become heated and to a certain extent reduced by the gases. The gas reduction of this material on the walls is enhanced by the scrubbing action of the swirling stream which removes inert gases (such as carbon dioxide) from the vicinity of the particles as soon as these gases are formed. Liquid phase reduction of this material on the walls also occurs, since the larger particles of carbon-containing material, i.e., coal are also thrown onto the walls where they can dissolve in the film of liquified ore, slag and partially reduced metal. Any very large particles of ore or carboncontaining material, i.e., coal may fall through the gas stream and travel as only partially liquified and reduced particles along the lower walls and out of the reduction zone to the hearth where they collect in a liquid pool. Slag is formed from the carbon-containing material, i.e., coal, ore and slag forming components both in the gas stream and on the reduction zone surface.

The reduction of particles borne in the gas stream takes about 3 to 20 seconds. (In the present specification, the term particles is used in its broad sense to include liquid droplets.) It is believed that in the gas stream the iron oxide melts first and then reduces to produce metallic iron, although the first iron nuclei formed may be porduced in the solid state. Since the liquid iron silicate phase has a considerably lower surface tension than the liquid iron, the liquid oxide would be expected to surround the liquid iron. The reducing gas reacts with the liquid oxide phase to remove oxygen, and a corresponding amount of iron is transferred to the iron sphere from the oxide phase. Thus, if this mechanism is correct, there is no slow, solid type of diffusion reaction as normally found in iron oxide reduction, and this is the reason that metallic iron is reduced quickly.

The matter on the walls of the reduction zone flows steadily along the walls being urged by the helically swirling gases. At the end of the reduction zone the molten matter is allowed to drip onto or flow into a hearth, which is preferably circular in plan view and where final liquid phase reduction of any unchanged ore occurs. The surface of the melt on the hearth is so situated that the hot gases continue to sweep over and supply heat to the melt. It is notable that the particles of matter and the slag being heated on the walls of the reduction Zone provide in effect, an insulating layer and decrease the heat losses which would otherwise occur by conduction to the furnace surroundings.

The process of this invention has the advantage that the fuel can be coal containing substantial quantities of impurities. This is because the heat generating process is complete before the resulting hot products of combustion come into contact with the ore and the remainder of the coal which is fed in with the ore is subjected to a high temperature gas stream which distils off its volatiles. Additional impurities are removed by the slag. An additional advantage of the process of the invention is that it largely avoids the lack of efiiciency obtained in blast furnace operations due to the necessity of forcing a large volume of gas through a thick bed of material and because of the formation of an insulating layer of carbon dioxide around metal oxide particles in blast furnace operation which slows down the reduction. Increased efficiency is also obtained by this invention in that relatively finely divided particles of ore can be treated with consequent rapid reduction. A further advantage of the process of the invention lies in its full utilization of all the available reduction Zone and hearth area thereby making it possible to obtain a large production with a small unit. Furthermore, the structure of an apparatus specially adapted to carry out the process of this invention is such that it can be closed down and started up far more readily than a blast furnace.

In the process of this invention, conditions of combustion in the cyclone burner can be chosen to be at their most effective without regard for the reducing conditions required in the reactor. The straight line configuration of apparatus will cut down refractory damage and allow heat transfer by radiation from the cyclone combustion zone into the reduction chamber. There is less tendency in this arrangement for the iron oxide to be thrown to the chamber walls before reduction. Since the reducing agent is added with the iron ore, hydrocarbons are available for the reduction reaction, especially in the case where solid fuels are used. This feature is in contrast to some other process where the immediate partial combustion of the fuel to produce the reducing atmosphere results in only minor quantities of hydrocarbons being available for the fast reduction reaction. The high alumina liquid ash produced by burning part of the coal used separately in the cyclone unit may be very valuable when utilized to coat the walls of the reaction chamber to obtain some protection for the refractory lining.

in the accompanying drawings,

FIGURE 1 is a schematic lay-out of a plant specially adapted to carry out the process of this invention;

FIGURE 2 is a sectional elevation view of an apparatus specifically adapted to carry out the process of this invention; and

FlGURE 3 is a section view on the line 3-3 of FIG- URE 2.

Referring now to FIGURE 1 of the drawings, coal feeder 1t and combustion air line 11 supply cyclone combustor 12 namely, a first zone providing the combustion Zone. A stream of hot gases from the combustion zone 12 is fed downstream to a zone 13. Coal, ore and lime are supplied to the second zone 13 by feeder 14, thereby converting zone 13 to a reducing zone. Slag and reduced metal are separately removed from reducing zone 13 at 15 and 16 respectively. The gases from cyclone combustor 12 which have passed through reducing zone 13 are directed by switch gate 17 alternately to stove 18 and 19, from whence they part successively to waste heat boiler 20, gas washer 21 and process gas recovery unit 22. Combustion air from compressor 23 is directed by switch 24 to whichever of units 18 and 19 is not in use so as to preheat the air which then passes to air line 11. Water is circulated by pump 25 through waste heat boiler 20 to provide process steam in steam return line 26.

Referring now to FIGURES 2 and 3 of the drawings, the coal feeder it which supplies fuel to cyclone combustor I2 is shown as being a hopper 27. Combustion air line 11 supplies air through distributor 28 to tangential dampers 29. The reduction zone 13 comprises a conically shaped portion 3!) diverging outwardly from re-entrant throat 43 of cyclone combustor I2 and a cylindrically shaped portion, the axis of which is in substantial alignment with the axis of cyclone combustor 12 and which is inclined downwardly in a direction away from cyclone combustor 12. At the lower end of reduction zone 13 there is a hearth 32 for reduced metal 33 and slag 34. Tap holes 35 and 36 are provided for the removal respectively of reduced metal and slag. The gases which have passed through the reducing zone are deflected by sloping end wall 37 up stack 38 from whence the gases pass to switch gate 17. Coal is fed into feeder 14 from hopper 39 by screw conveyor 49. Similarly a mixture of ore and limestone is fed from hopper 41 by screw conveyor 42 to feeder 14. The use of two conveyors permits rapid adjustment of reducing conditions in the reducing zone to control the quality of the end product.

The preferred diamete of the cylindrical portion 31 of the reauction zone is about twice the diameter of the cyclone combustor and the length of the reduction zone including both conically shaped portion 30 and cylindrically shaped portion 31 is about three times the diameter of the cyclone combustor. The distance from the mouth of cyclone combustor 12 to end wall 37 is about four times the diameter of the cyclone combustor.

The preferred proportions of the feed to the smelting unit are as follows (calculated on the basis of a thousand pounds of ore):

Lbs.

Ore 1000 Limestone 200 Lbs. Coal to cyclone 500 Coal to reduction zone 100 Oxygen to cyclone 700 It will be appreciated that there may be considerable variations in the foregoing proportions depending on variables such as the nature of the ore, the nature of the fuel and the temperature of the gases issuing from the cyclone combustor.

The analysis of a typical ore is as follows:

F6203 .5 FeO 0.5 M11304 A1 0 2.4 Si0 4.6 H 0 8.0 MgO 0.4 CO 0.1

A typical analysis for the limestone is as follows:

F6203 0.6 A1 0 2.3 SiHO 7.4 H 9 0.9 MgO 1.3 CO 38.8 CaO 47.7

Loss on ignition 39.5%

An analysis of a typical coal is as follows: C 68.2

S 6.1 N 1.2 O 4.8

H 0 2.1 Ash 12 7 The estimated analysis of the mineral matter in the above coal is as follows:

Total heating energy of the coal 12,310 B.t.u./lb.

The hot gases issuing from the cyclone combustor will be at a temperature in excess of 3000 F. The extent to which reduction occurs in the gas phase will depend on variables such as the size and value of the materials, the size of the equipment, the atmosphere of and the temperature of the gas stream issuing from the cyclone and the velocity of the cyclone, but it may rise as high as 80% of the total reduction of metal oxides in the case 6 of an iron ore and should be at least 50%. About half or more of the sulphur content of the coal fed to the reduction zone will be distilled or burnt off while the coal is falling through the reduction zone. The fuel, the ore and the slag forming components should be supplied to the equipment in finely divided form. It is preferred that each of the foregoing materials have an appropriate screen analysis of 100% minus A1", 50% minus 50 mesh (Tyler) and 20% minus 200 mesh, Where an eight foot diameter cyclone is employed.

The ash from coal burnt by the cyclone combustor will automatically be disposed of since it will pass into the slag.

Substantially 100% recovery of reduced metal should be obtained from the ore.

The conditions under which smelting is carried out can be varied to produce a crude steel. Lowering of the carbon content of the metal will be favoured by decreasing the amount of coal supplied to the reaction zone. In this case, most of the reduction will be achieved by carbon monoxide gas and there will be little pick up of carbon by the metal. The foregoing may be accompanied by a slight dropping off of the recovery of reduced metal.

I claim:

1. The process of reducing a metal oxide in an ore comprising the steps, in sequence, of:

(1) continuously feeding a carbon-containing material to a combustion zone;

(2) completely burning said carbon-containing material in said combustion zone in a helically swirling stream to produce combustion products consisting essentially of CO and H 0 said combustion products being at a temperature in excess of 3000 F.;

(3) passing said combustion products in a swirling stream and while still at a temperature in excess of 3000 F. into a second zone;

(4) continuously feeding a finely divided mixture of ore containing metal oxide, slag forming constituents, and carbon-containing material into said stream of hot combustion products in said second zone downstream of said entry point of said hot combustion products thereby converting said second zone into a reducing zone;

(5) continuously reacting said mixture in said stream in said reducing zone whereby at least 50% of the metal oxide is reduced to metal and wherein slag forming constituents are melted;

(6) continuously collecting liquids and solids separating from said stream as a mixture of slag, ore, carbon-containing material and metal;

(7) continuously passing said swirling stream 'over the surface of said mixture thereby completing reduction of the metal oxide in said ore to metal; and finally (8) continuously recovering the thereby produced metal.

2. The process of claim 1 where each of said carboncontaining materials is powdered coal.

3. The process of claim 2 in which the metal oxide in the ore is predominantly iron oxide.

References Cited by the Examiner UNITED STATES PATENTS Re. 12,424 12/05 Brown -26 817,414 4/06 Brown 75-26 DAVID L. RECK, Primary Examiner. 

1. THE PROCESS OF REDUCING A METAL OXIDE IN AN ORE COMPRISING THE STEPS, IN SEQUENCE, OF: (1) CONTINUOUSLY FEEDING A CARBON-CONTAINING MATERIAL TO A COMBUSTION ZONE; (2) COMPLETELY BURNING SAID CARBON-CONTAINING MATERIAL IN SAID COMBUSTION ZONE IN A HELICALLY SWIRLING STREAM TO PRODUCE COMBUSTION PROUDCTS CONSISTING ESSENTIALLY OF XO2 AND H2O SAID COMBUSTION PRODUCTS BEING AT A TEMPERATURE IN EXCESS OF 3000*F.; (3) PASSING SAID COMBUSTION PRODUCTS INA SWIRLING STREAM AND WHILE STILL AT A TEMPERATURE IN EXCESS OF 3000*F. INTO A SECOND ZONE; (4) CONTINUOUSLY FEEDING A FINELY DIVIDED MIXTURE OF ORE CONTAINING METAL OXIDE, SLAG FORMING CONSTITUENTS, AND CARBON-CAONTAINING MATERIAL INTO SAID STREAM OF HOT COMBUSTION PRODUCTS IN SAID SECOND ZONE DOWNSTREAM OF SAID ENTRY POINT OF SAID HOT COMBUSTION PRODUCTS THEREBY CONVERTING SAID SECOND ZONE INTO A REDUCING ZONE; (5) CONTINUOUSLY REACTNG SAID MIXTURE IN SAID STREAM IN SAID REDUCING ZONE WHEREBY AT LEAST 50% OF THE METAL OXIDE IS REDUCED TO METAL AND WHEREIN SLAG FORMING CONSTITUENTS ARE MELTED; (6) CONTINUOUSLY COLLECTING LIQUIDS AND SOLIDS SEPARATING FROMSAID STREAM AS A MIXTURE OF SLAG, ORE, CARBON-CONTAINING MATERIAL AND METAL; (7) CONTINUOUSLY PASSING SAID SWIRLING STREAM OVER THE SURFACE OF SAID MIXTURE THEREBY COMPLETING REDUCTION OF THE METAL OXIDE IN SAID ORE TO METAL; AND FINALLY (8) CONTINUOUSLY RECOVERING THE THEREBY PRODUCED METAL. 